The origin of mass is one of the most intriguing mysteries of nature. Some particles, such as the W boson (which carries the weak force) have so much mass they barely move, while others, like the photon, are entirely massless and zip around at the speed of light.

What is it that makes one particle light and another heavy?

The mass of fundamental particles – those that carry forces and build nuclei and atoms – is often explained by the way they move through an invisible "Higgs field" that is thought to pervade the vacuum of space.

To some particles, such as the top quark, the Higgs field is like molasses: they get bogged down and become very heavy. To others, like the photon, the field is empty space: they fly through unimpeded and gain no weight at all.

In this exclusive video, our kid Brian Cox explains how giant particle colliders like the Large Hadron Collider at Cern near Geneva, are closing in on the elusive Higgs particle. When and if they do, the puzzle of mass will be solved.